1. Field of the Invention
The present invention relates generally to ink-jet technology and, more particularly, to methods and apparatus for producing hard copy with modular ink-jet hard copy devices and systems.
2. Description of Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
Fundamentally, FIG. 1 (PRIOR ART) depicts an ink-jet hard copy apparatus, in this exemplary embodiment a computer peripheral printer, 101. A housing 103 encloses the electrical and mechanical operating mechanisms of the printer 101. Generally, operation is directed by an electronic controller (usually a microprocessor or application specific integrated circuit ("ASIC") controlled printed circuit board, not shown) connected by appropriate cabling to a computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions and data processing logic with firmware or software instructions. Cut-sheet print media 105, loaded by the end-user onto an input tray 107, is fed by a suitable internal paper-path transport mechanism (not shown) to a printing station where graphical or photographical images and alphanumeric text is created. A carriage 109, mounted on a slider rod 111, scans the print medium. An encoder strip 113 is provided for keeping track of the position of the carriage 109 at any given time. A set 115 of individual ink-jet pens, or print cartridges, 117A-117D is releasably mounted into the carriage 109 for easy access (generally, in a full color system, inks for the subtractive primary colors, cyan, yellow, magenta (CMY) and true black (K) are provided). Once a printed page is completed, the print medium is ejected by the transport mechanism onto an output tray 119.
At the heart of an ink-jet hard copy apparatus is the writing instrument itself, commonly called a "print cartridge" or a "pen." As shown in FIG. 2 (the subject of separate patent applications assigned to the assignee of the present invention), an exemplary ink-jet pen 210 includes a body, or shell, 212 that encases an ink reservoir, or an ink accumulator chamber and related print-head pressure regulator mechanisms (not shown), containing either fluid ink or hot melt type printing fluid. A print head 214 includes a nozzle plate 216 having a plurality of small (e.g., diameter approximately twenty .mu.m) orifices 217 from which tiny droplets of ink (e.g., approximately ten picoliters) are ejected onto adjacent print media as the pen(s) scan across a printing zone at a high speed (approximately 25 inches per second, "ips"), depositing ink droplets in patterns that through dot matrix manipulation form alphanumeric text characters or graphic images. A flex circuit 218 includes electrical contacts 220 for connecting the pen 210 to the electronic controller. The print head elements have a limited life due to electrical, thermodynamic, and fluid dynamic loads imposed during operation. Thus, in the current state of the art, a costly and functionally significant portion of the writing system must be replaced with each print cartridge change.
The apparatus elements directly involved with inking a print media--in other words, all components of the system which come into contact with ink other than the print media itself--are referred to hereinafter as a writing engine; non-writing elements of the hard copy apparatus system are referred to hereinafter as a hard copy engine. Cartridges, pens, ink-reservoirs, and the like are referred to as ink-jet consumables. (Use of these terms is for convenience of description and is not intended as any limitation to the scope of the invention, nor should any such intention or limitation be implied therefrom.)
Having become commercially practicable in the early 1980's, ink-jet technology is a relatively young field of invention. In state-of-the-art thermal ink-jet systems, two complementary writing instruments have become commercially viable. The first is the disposable print cartridge type; the second is the semipermanent print head pen type.
The disposable writing instrument has a self-contained reservoir ("on-axis" or "on-board;" generally meaning on the pen carriage subsystem) for storing ink and providing appropriate amounts of ink to the print head during a printing or servicing cycle throughout the life of the writing instrument. When out of ink, the entire print cartridge is replaced by the end-user.
When ink-jet technology was in its early stages, print head life expectancy was more or less equivalent to the amount of ink that was held in the on-board ink reservoir. More recently, advances in the state-of-the-art for print head design and manufacture has led to a longer operational life expectancy for the print head than can be used with a reasonably-sized, non-replaceable ink reservoir. Thus, the development and commercialization of a second commercial type using a replaceable ink writing subsystem that employs a semi-permanent printing element, where the ink is supplied to the print head mechanism from a replaceable ink reservoir located either on-axis or "off-axis," (with respect to the pen carriage subsystem), such as a biased ink bladder or bag (see e.g., U.S. Pat. No. 5,359,353 (Hunt et al.) assigned to the common assignee of the present invention and incorporated herein by reference). This second type of writing instrument, the semipermanent pen, can also include mechanisms for regulating both requisite print head back pressure (in a free-ink ink-jet writing instrument) and the flow of ink from the off-board ink reservoir to the pen (shown in FIG. 2 as having an ink inlet mechanism 222 that would be coupled 223 to the replaceable or refillable off-axis ink supplies 224). In the off-axis type of hard copy apparatus, separate, replaceable or refillable, ink reservoirs are located within the fixed apparatus housing 103, FIG. 1, and appropriately coupled to the moving pen set 115 via ink conduits, such as tubes that are impervious to the ink chemicals. In the on-axis type of hard copy apparatus, separate, replaceable or refillable, ink reservoirs couple to the print head ink interface directly and are located on the moving pen carriage system.
Each commercial configuration has advantages and disadvantages. The disposable print cartridge type writing instrument is simple and easy to use but costly, as the relatively expensive print head mechanism is discarded along with the on-axis ink chamber once the ink is fully consumed. Moreover, the non-replaceable on-axis ink chamber in and of itself inherently limits the number of pages which can be printed due to its relatively small ink capacity. With the increase in print head longevity, end users have turned to refill kits or lower cost re-manufactured print cartridges that are less expensive than replacement with a new print cartridge. The use of ink refill kits is often a messy task. Still further, the need and desire for even less expensive ink continues to grow. The recent commercialization of near photographic quality ink-jet printing has increased the end user's consumption of ink much faster than in the past when simple text and color graphics imagery was the norm. Even traditional business documents are now including more images and complex graphics, thus consuming more ink. Naturally, end user replacement costs increase.
The semipermanent pen type system is potentially more economical to the end-user. The on-axis, replaceable, ink subsystem offers lower cost per page printing, but the end user is required to replace smaller ink reservoirs more often than with off-axis implementations. This is due to the physical limitation of how much ink can be reasonably carried on the carriage system. Similar to the disposable print cartridge system, there are also throughput and size penalties due to the mass and volume of the on-axis ink reservoirs. The off-axis ink reservoir type hard copy apparatus potentially can have a smaller carriage and offer larger ink reservoir; the penalty is a more complex design, including additional intra-apparatus ink delivery mechanisms which add cost. The benefits of the larger ink reservoir are in potentially higher throughout due to a lower mass carriage, lower user intervention rates, and even lower cost per page. In a full color hard copy system using a plurality of semipermanent pens, a plurality of off-axis ink reservoirs, and a concomitant set of interconnects, if a printing error occurs, the source of the problem can be difficult to locate. End-user diagnosis may be impossible unless the manufacturer provides expensive troubleshooting technology. Changes in ink formulation--either by the original equipment manufacturer or by a second source using cheaper materials and chemicals--can result in an end-user inadvertently replacing a reservoir with an incompatible model, again resulting in printing errors or even catastrophic equipment failures. Still further, in some implementations certain elements of the writing subsystem are not replaced with the ink supply, such as reservoir-to-pen tubing, valves, and the like; thus, design criteria--including ink chemical formulations--must be employed so that these elements have a life expectancy as great as that of the hard copy engine components.
Moreover, all of the above configurations require a costly, permanent (i.e., matching the hard copy system life expectancy), service station which includes the primary functions of wiping print head nozzle orifices of pooled ink (wiper(s)), collecting waste ink (spittoon(s)), and providing print head protection by capping during non-use (caps or capping devices). While seemingly a simple device, ink-jet service station technology presents many design challenges. Non-replaceable servicing elements must be designed to last the lifetime of the hard copy engine. For example, design constraints are placed on both product size and printing element servicing algorithms due to the limited capacity of a permanent spittoon. The spittoon must be large enough to hold ink residue from all of the servicing operations over the lifetime of the hard copy engine, not just the writing engine. This limits the volume of ink which can be spit during each service interval. Limiting the amount of ink for print head servicing limits the design flexibility for writing instruments. Furthermore, extended usage can cause some of the servicing elements, namely the cap and wiper to fatigue and wear out, or the spittoon to cake and become a problem. Note also, that print head failures, such as leaking ink, can make the servicing elements inoperable; failed servicing components can cause failures in any new writing instrument subsequently installed. Moreover, if a new print cartridge contains an ink that is incompatible with ink which has been left on the servicing elements from a previous print cartridge, the new print cartridge may fail due to ink contamination from the service station. By not replacing the servicing elements with each new print cartridge, the choice of future inks is limited by the composition of past ink usage. Thus, permanent service stations raise manufacturing and support costs.
One key to the commercial success of both disposable print cartridge and semipermanent pen ink-jet printing systems is the high print quality--approaching photographic, electrophotographic, and laser printing quality--at a relatively low cost achieved through the use of replaceable printing elements. While it is commercially known to package and sell ink-jet components together, the present invention provides a concept using a new approach to both the ink-jet consumables and the hard copy apparatus. The goal is to obtain the benefits of both disposable and off-axis ink-jet technologies without the associated disadvantages of each. As Such re-partitioning of state-of-the-art ink-jet printing components and functions within an ink-jet hard copy apparatus is undertaken.